(a) Field of the Invention
The present invention relates to an organic light emitting diode display and a method for manufacturing the same.
(b) Description of the Related Art
Recent trends towards lightweight and thin personal computers and television sets require lightweight and thin display devices, and flat panel displays satisfying such requirements are being substituted for conventional cathode ray tubes (CRT).
The flat panel displays may include a liquid crystal display (LCD), a field emission display (FED), an organic light emitting diode (OLED) display, a plasma display panel (PDP), and so on. Among the flat panel displays, the OLED display is the most promising because of its low power consumption, fast response time, wide viewing angle, and high contrast ratio.
An OLED display is a self-emissive display device that includes two electrodes and an organic light emitting layer interposed therebetween. One of the two electrodes injects holes and the other of the two electrodes injects electrons into the light emitting layer. The injected electrons and holes are combined to form exitons, and the exitons emit light as discharge energy.
The OLED displays may be categorized by their driving method into passive matrix OLED displays and active matrix OLED displays. The passive matrix OLED display includes a plurality of anode lines, a plurality of cathode lines intersecting the anode lines, and a plurality of pixels, each including a light emission layer. The selection of one of the anode lines and one of the cathode lines causes light emission of the pixel located at the intersection of the selected signal lines. The active matrix OLED display includes a plurality of pixels, each including a switching transistor, a driving transistor, and a storage capacitor, as well as an anode, a cathode, and a light emission layer. The driving transistor receives a data voltage from the switching transistor and drives a current having a magnitude depending on the data voltage, and the current from the driving transistor enters the light emission layer to cause light emission having intensity depending on the current.
Characteristics of the switching transistor and the driving transistor for optimizing characteristics of the OLED display are different from each other. That is, the switching transistor requires a high current on/off characteristic Ion/Ioff, while the driving transistor requires high mobility and high stability for flowing sufficient current to the OLED.
When an off current of the switching transistor increases, a data voltage applied to the driving transistor decreases such that cross-talk may occur. In addition, when the mobility and the stability of the driving transistor are low, the current amount flowing to the OLED decreases such that the amount of light emitted by the OLED decreases, image sticking occurs, and the lifetime of the OLED is reduced.